As for the big guy, he's just loving this. And from a big evil bastard's perspective, why shouldn't he? His original plan to kidnap Peach twenty-three years ago has turned into the gift that keeps on giving. He just wanted control over the kingdom, but what he ended up with turned out to be far more satisfying.
He might not be sitting on a throne overtly ruling with an iron fist, but he's got absolute power in a way far more appealing to a vindictive lizardy git like himself. He's got Peach coming running to him like the secretly needy primadonna cheerleader runs to her gruff jock boyfriend for all kinds dubious 'approval'. A staged kidnapping attempt every couple of years allows him to secretly keep his dirty, claw-tipped fingers in all manner of pies without alerting suspicion, despite his bizarrely turning up at every kart race and party and acting like an old buddy. (What, you think after all that practice his schemes would still be legitimately failing two decades later? And you never wondered about the lack of animosity?) And most satisfying of all, he gets to see the perpetually cock-blocked plumber come blindly charging in to 'save' Peach, and gets to watch him walk away actually thinking he's won. Every. Single. Time
Oh how Bowser laughs after the end credits roll, and it's all thanks to Stockholm Syndrome. What a delightful little psychological disorder it is.